1. Field of the Invention
The present invention relates to an internal combustion engine for a vehicle, and more particularly to a control device for an internal combustion engine that includes a first fuel injection mechanism (in-cylinder injector) injecting fuel into a cylinder and a second fuel injection mechanism (intake manifold injector) injecting fuel into an intake manifold or an intake port.
2. Description of the Background Art
An internal combustion engine provided with an intake manifold injector for injecting fuel into an intake manifold and an in-cylinder injector for injecting fuel into a combustion chamber, in which fuel injection from the intake manifold injector is stopped when load of the engine is lower than preset load and fuel injection from the intake manifold injector is allowed when load of the engine is higher than the preset load, is known. Generally, such an internal combustion engine includes an intake manifold injector and an in-cylinder injector in each cylinder.
Though different from the internal combustion engine having such two types of injectors, there is an internal combustion engine in which fuel injection into each cylinder is performed twice prior to one expansion stroke. For example, there is a diesel engine in which a small amount of fuel is supplied to a combustion chamber in pilot injection prior to main fuel injection and the fuel injected in pilot injection is burnt prior to main fuel injection, so that ignition delay of the fuel injected in main fuel injection is decreased, thereby preventing increase in combustion noise (knocking noise) of the internal combustion engine. A control device for such a diesel engine is represented by a fuel injection control device disclosed in Japanese Patent Laying-Open No. 2004-27910. A fuel injection apparatus includes an accumulator for storing a high-pressure fuel and a fuel injection valve connected to the accumulator and injecting the fuel stored in the accumulator into the combustion chamber of the internal combustion engine, and pilot injection from the fuel injection valve is performed prior to main fuel injection. A fuel injection control device includes pulsation detection means for detecting fluctuation in a pressure of fuel supplied to the fuel injection valve that is caused by pilot injection and correction means for calculating variation in fuel injection performance of the fuel injection valve in pilot injection based on fluctuation in the pressure and correcting an amount of fuel injection in pilot injection based on variation in the fuel injection performance such that an actual fuel injection amount in next pilot injection attains a target pilot injection amount. The correction means corrects an amount of fuel injection in main fuel injection based on calculated variation in the pilot injection performance such that an actual fuel injection amount in main fuel injection attains a target main fuel injection amount.
According to the fuel injection control device, in what is called a common rail type fuel injection apparatus including an accumulator (common rail) storing high-pressure fuel, fluctuation in the fuel pressure involved in pilot injection is detected, and variation in the fuel injection performance of each fuel injection valve during pilot fuel injection is calculated based on detected pressure fluctuation. For example, when pilot injection is performed, the pressure of fuel within a system fluctuates depending on an amount of fuel injection. Accordingly, if the amount of pilot fuel injection is reduced due to wear of a valve seat or the like, magnitude of fuel pressure fluctuation within the system at the time of pilot fuel injection is also made smaller. Therefore, variation in the fuel injection performance such as the amount of fuel injection can thus be calculated based on fluctuation in the fuel pressure during pilot fuel injection, and an injection instruction signal is corrected so as to increase an actual fuel injection amount by that variation (lowered amount), whereby the actual pilot fuel injection amount can accurately attain the target value. In addition, the amount of fuel injection is corrected also in main fuel injection, so as to further ensure prevention of deterioration in exhaust performance or generation of smoke.
The fuel injection valve provided in each cylinder and injecting fuel into the cylinder, as disclosed in Japanese Patent Laying-Open No. 2004-27910, is used to perform pilot injection and main fuel injection. The fuel injection valve injecting fuel into the cylinder, however, is provided in such a manner that its tip end projects within the combustion chamber. Accordingly, deposits may adhere to an injection hole and the fuel may not properly be injected. In such a case, a desired amount of fuel can be injected neither in pilot injection nor in main fuel injection disclosed in Japanese Patent Laying-Open No. 2004-27910, and the internal combustion engine cannot exhibit desired performance.